The studies of this project include those of the ongoing development and application of an in vivo experimental animal model system using juvenile sheep for evaluating cardiac valves. The studies are multidisciplinary in nature, using investigative techniques from the fields of surgery, physiology, pathology engineering, and technology development. Major emphases during the year have been: 1) studies of the efficacy of preimplantation treatment regimens upon ameliorating the calcification of bioprosthetic valves; 2) definitions of the velocity, flow and turbulence profiles produced by prosthetic valves using ultrasound techniques; 3) comparisons of fluid dynamic data obtained from the in vivo (animal) studies and those obtained from in vitro studies; 4) comparisons of old generation (introduced prior to 1975) versus new generation - valves; 5)comparative hemodynamic/fluid mechanic studies of prosthetic valves used clinically or undergoing preclinical evaluations; 6) continuing characterization of the morphologic pathologic alterations occurring in bioprosthetic valves; and 7) refinements of operative and postoperative management techniques.